Early fall is a nightmare for hurricane risk.  I cancelled a Pacific Northwest visit that would have been during Irma cleanup days.  Instead did Irma in Washington, which was fun in a distracted sort of way.   Felt weird to walk up to the Botanic Garden and be welcomed by a big bed of Florida Gulf coast beach sunflowers.  Still, early fall might have decent air fares and decent travel insurance costs.

Cornwall and London were fine in early June.  Newquay had decent surf.  I had an eye infection.  My sense is that European vacations (and heat waves) might be August-heavy.  Ask about UK and French school schedules?  

Versailles has a helpful online calendar predicting busy days.  I suspect you'd be visiting something other than the biggest historic theme park in France, but between them and Disney Paris, you might get some sense of crowd factor. Perhaps better yet, I think you're in the middle of a thicket of quality first-hand information on non-surf tourism in France.  

For beach-related info, the British are such inveterate surf tourists that I expect plenty in print and on video.  

Not exactly relevant, but Portugal and Galicia are burning.  Severe Weather Europe.  Photos are horrifying.

A lot of smoke was sucked by Ophelia over western France and into England.

A side trip, sort of, is drive through south of France then over to milano... can visit beautiful alps one way drive through mont blanc tunnel & by coast other way ( Cannes etc). The reason I mention other than personal bias - Milan is one of my favorite cities - is the new Emirates flight MXP-JFK! If you play your dates right you can get that flight for around 300 euros each way from JFK which might save bit money!!! And it's a good flight unlike American cattle cart airlines. 

Now, a lot of people worry about driving in that part of Europe,  but IMHO it's not really that big of deal just remember 2 things:

1st In Italy drive fast & look in rearview so when see sports car coming up behind you can move out of the passing lane. But don't drive in milano, rather stay by mxp airport where hotels let park for free and can take 30 minute train from mxp into city. ANd 2nd Gas isn't cheap, budget for it 

get up early and go surf - it'll make that hangover go away and/or make the workday more tolerable :)